BS
I did just that - Downloaded W7 and upgraded a Vista system. You have to be sure that you are installing like for like. eg. Home premium for home premium. It worked fine for me but you may have to search for the odd drivers for perhaps printer or scanner. Having said that W7 is pretty good at finding any driver that it needs. This ugrade will leave your programmes and data in tact. However i would back up you data just in case!